/**
 * @file
 * MQTT client
 *
 * @defgroup mqtt MQTT client
 * @ingroup apps
 * @verbinclude mqtt_client.txt
 */

/*
 * Copyright (c) 2016 Erik Andersson <erian747@gmail.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack
 *
 * Author: Erik Andersson <erian747@gmail.com>
 *
 *
 * @todo:
 * - Handle large outgoing payloads for PUBLISH messages
 * - Fix restriction of a single topic in each (UN)SUBSCRIBE message (protocol has support for multiple topics)
 * - Add support for legacy MQTT protocol version
 *
 * Please coordinate changes and requests with Erik Andersson
 * Erik Andersson <erian747@gmail.com>
 *
 */
#include "lwip/apps/mqtt.h"
#include "lwip/timeouts.h"
#include "lwip/ip_addr.h"
#include "lwip/mem.h"
#include "lwip/err.h"
#include "lwip/pbuf.h"
#include "lwip/tcp.h"
#include <string.h>

#if LWIP_TCP && LWIP_CALLBACK_API

/**
 * MQTT_DEBUG: Default is off.
 */
#if !defined MQTT_DEBUG || defined __DOXYGEN__
	#define MQTT_DEBUG                  LWIP_DBG_OFF
#endif

#define MQTT_DEBUG_TRACE        (MQTT_DEBUG | LWIP_DBG_TRACE)
#define MQTT_DEBUG_STATE        (MQTT_DEBUG | LWIP_DBG_STATE)
#define MQTT_DEBUG_WARN         (MQTT_DEBUG | LWIP_DBG_LEVEL_WARNING)
#define MQTT_DEBUG_WARN_STATE   (MQTT_DEBUG | LWIP_DBG_LEVEL_WARNING | LWIP_DBG_STATE)
#define MQTT_DEBUG_SERIOUS      (MQTT_DEBUG | LWIP_DBG_LEVEL_SERIOUS)

static void mqtt_cyclic_timer(void* arg);

/**
 * MQTT client connection states
 */
enum {
	TCP_DISCONNECTED,
	TCP_CONNECTING,
	MQTT_CONNECTING,
	MQTT_CONNECTED
};

/**
 * MQTT control message types
 */
enum mqtt_message_type {
	MQTT_MSG_TYPE_CONNECT = 1,
	MQTT_MSG_TYPE_CONNACK = 2,
	MQTT_MSG_TYPE_PUBLISH = 3,
	MQTT_MSG_TYPE_PUBACK = 4,
	MQTT_MSG_TYPE_PUBREC = 5,
	MQTT_MSG_TYPE_PUBREL = 6,
	MQTT_MSG_TYPE_PUBCOMP = 7,
	MQTT_MSG_TYPE_SUBSCRIBE = 8,
	MQTT_MSG_TYPE_SUBACK = 9,
	MQTT_MSG_TYPE_UNSUBSCRIBE = 10,
	MQTT_MSG_TYPE_UNSUBACK = 11,
	MQTT_MSG_TYPE_PINGREQ = 12,
	MQTT_MSG_TYPE_PINGRESP = 13,
	MQTT_MSG_TYPE_DISCONNECT = 14
};

/** Helpers to extract control packet type and qos from first byte in fixed header */
#define MQTT_CTL_PACKET_TYPE(fixed_hdr_byte0) ((fixed_hdr_byte0 & 0xf0) >> 4)
#define MQTT_CTL_PACKET_QOS(fixed_hdr_byte0) ((fixed_hdr_byte0 & 0x6) >> 1)

/**
 * MQTT connect flags, only used in CONNECT message
 */
enum mqtt_connect_flag {
	MQTT_CONNECT_FLAG_USERNAME = 1 << 7,
	MQTT_CONNECT_FLAG_PASSWORD = 1 << 6,
	MQTT_CONNECT_FLAG_WILL_RETAIN = 1 << 5,
	MQTT_CONNECT_FLAG_WILL = 1 << 2,
	MQTT_CONNECT_FLAG_CLEAN_SESSION = 1 << 1
};


#if defined(LWIP_DEBUG)
static const char* const mqtt_message_type_str[15] = {
	"UNDEFINED",
	"CONNECT",
	"CONNACK",
	"PUBLISH",
	"PUBACK",
	"PUBREC",
	"PUBREL",
	"PUBCOMP",
	"SUBSCRIBE",
	"SUBACK",
	"UNSUBSCRIBE",
	"UNSUBACK",
	"PINGREQ",
	"PINGRESP",
	"DISCONNECT"
};

/**
 * Message type value to string
 * @param msg_type see enum mqtt_message_type
 *
 * @return Control message type text string
 */
static const char*
mqtt_msg_type_to_str(u8_t msg_type)
{
	if(msg_type >= LWIP_ARRAYSIZE(mqtt_message_type_str)) {
		msg_type = 0;
	}

	return mqtt_message_type_str[msg_type];
}

#endif


/**
 * Generate MQTT packet identifier
 * @param client MQTT client
 * @return New packet identifier, range 1 to 65535
 */
static u16_t
msg_generate_packet_id(mqtt_client_t* client)
{
	client->pkt_id_seq++;

	if(client->pkt_id_seq == 0) {
		client->pkt_id_seq++;
	}

	return client->pkt_id_seq;
}

/*--------------------------------------------------------------------------------------------------------------------- */
/* Output ring buffer */


#define MQTT_RINGBUF_IDX_MASK ((MQTT_OUTPUT_RINGBUF_SIZE) - 1)

/** Add single item to ring buffer */
#define mqtt_ringbuf_put(rb, item) ((rb)->buf)[(rb)->put++ & MQTT_RINGBUF_IDX_MASK] = (item)

/** Return number of bytes in ring buffer */
#define mqtt_ringbuf_len(rb) ((u16_t)((rb)->put - (rb)->get))

/** Return number of bytes free in ring buffer */
#define mqtt_ringbuf_free(rb) (MQTT_OUTPUT_RINGBUF_SIZE - mqtt_ringbuf_len(rb))

/** Return number of bytes possible to read without wrapping around */
#define mqtt_ringbuf_linear_read_length(rb) LWIP_MIN(mqtt_ringbuf_len(rb), (MQTT_OUTPUT_RINGBUF_SIZE - ((rb)->get & MQTT_RINGBUF_IDX_MASK)))

/** Return pointer to ring buffer get position */
#define mqtt_ringbuf_get_ptr(rb) (&(rb)->buf[(rb)->get & MQTT_RINGBUF_IDX_MASK])

#define mqtt_ringbuf_advance_get_idx(rb, len) ((rb)->get += (len))


/**
 * Try send as many bytes as possible from output ring buffer
 * @param rb Output ring buffer
 * @param tpcb TCP connection handle
 */
static void
mqtt_output_send(struct mqtt_ringbuf_t* rb, struct tcp_pcb* tpcb)
{
	err_t err;
	u8_t wrap = 0;
	u16_t ringbuf_lin_len = mqtt_ringbuf_linear_read_length(rb);
	u16_t send_len = tcp_sndbuf(tpcb);
	LWIP_ASSERT("mqtt_output_send: tpcb != NULL", tpcb != NULL);

	if(send_len == 0 || ringbuf_lin_len == 0) {
		return;
	}

	LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_output_send: tcp_sndbuf: %d bytes, ringbuf_linear_available: %d, get %d, put %d\n",
	                               send_len, ringbuf_lin_len, ((rb)->get & MQTT_RINGBUF_IDX_MASK), ((rb)->put & MQTT_RINGBUF_IDX_MASK)));

	if(send_len > ringbuf_lin_len) {
		/* Space in TCP output buffer is larger than available in ring buffer linear portion */
		send_len = ringbuf_lin_len;
		/* Wrap around if more data in ring buffer after linear portion */
		wrap = (mqtt_ringbuf_len(rb) > ringbuf_lin_len);
	}

	err = tcp_write(tpcb, mqtt_ringbuf_get_ptr(rb), send_len, TCP_WRITE_FLAG_COPY | (wrap ? TCP_WRITE_FLAG_MORE : 0));

	if((err == ERR_OK) && wrap) {
		mqtt_ringbuf_advance_get_idx(rb, send_len);
		/* Use the lesser one of ring buffer linear length and TCP send buffer size */
		send_len = LWIP_MIN(tcp_sndbuf(tpcb), mqtt_ringbuf_linear_read_length(rb));
		err = tcp_write(tpcb, mqtt_ringbuf_get_ptr(rb), send_len, TCP_WRITE_FLAG_COPY);
	}

	if(err == ERR_OK) {
		mqtt_ringbuf_advance_get_idx(rb, send_len);
		/* Flush */
		tcp_output(tpcb);
	} else {
		LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_output_send: Send failed with err %d (\"%s\")\n", err, lwip_strerr(err)));
	}
}



/*--------------------------------------------------------------------------------------------------------------------- */
/* Request queue */

/**
 * Create request item
 * @param r_objs Pointer to request objects
 * @param pkt_id Packet identifier of request
 * @param cb Packet callback to call when requests lifetime ends
 * @param arg Parameter following callback
 * @return Request or NULL if failed to create
 */
static struct mqtt_request_t*
mqtt_create_request(struct mqtt_request_t* r_objs, u16_t pkt_id, mqtt_request_cb_t cb, void* arg)
{
	struct mqtt_request_t* r = NULL;
	u8_t n;
	LWIP_ASSERT("mqtt_create_request: r_objs != NULL", r_objs != NULL);

	for(n = 0; n < MQTT_REQ_MAX_IN_FLIGHT; n++) {
		/* Item point to itself if not in use */
		if(r_objs[n].next == &r_objs[n]) {
			r = &r_objs[n];
			r->next = NULL;
			r->cb = cb;
			r->arg = arg;
			r->pkt_id = pkt_id;
			break;
		}
	}

	return r;
}


/**
 * Append request to pending request queue
 * @param tail Pointer to request queue tail pointer
 * @param r Request to append
 */
static void
mqtt_append_request(struct mqtt_request_t** tail, struct mqtt_request_t* r)
{
	struct mqtt_request_t* head = NULL;
	s16_t time_before = 0;
	struct mqtt_request_t* iter;

	LWIP_ASSERT("mqtt_append_request: tail != NULL", tail != NULL);

	/* Iterate trough queue to find head, and count total timeout time */
	for(iter = *tail; iter != NULL; iter = iter->next) {
		time_before += iter->timeout_diff;
		head = iter;
	}

	LWIP_ASSERT("mqtt_append_request: time_before <= MQTT_REQ_TIMEOUT", time_before <= MQTT_REQ_TIMEOUT);
	r->timeout_diff = MQTT_REQ_TIMEOUT - time_before;

	if(head == NULL) {
		*tail = r;
	} else {
		head->next = r;
	}
}


/**
 * Delete request item
 * @param r Request item to delete
 */
static void
mqtt_delete_request(struct mqtt_request_t* r)
{
	if(r != NULL) {
		r->next = r;
	}
}

/**
 * Remove a request item with a specific packet identifier from request queue
 * @param tail Pointer to request queue tail pointer
 * @param pkt_id Packet identifier of request to take
 * @return Request item if found, NULL if not
 */
static struct mqtt_request_t*
mqtt_take_request(struct mqtt_request_t** tail, u16_t pkt_id)
{
	struct mqtt_request_t* iter = NULL, *prev = NULL;
	LWIP_ASSERT("mqtt_take_request: tail != NULL", tail != NULL);

	/* Search all request for pkt_id */
	for(iter = *tail; iter != NULL; iter = iter->next) {
		if(iter->pkt_id == pkt_id) {
			break;
		}

		prev = iter;
	}

	/* If request was found */
	if(iter != NULL) {
		/* unchain */
		if(prev == NULL) {
			*tail = iter->next;
		} else {
			prev->next = iter->next;
		}

		/* If exists, add remaining timeout time for the request to next */
		if(iter->next != NULL) {
			iter->next->timeout_diff += iter->timeout_diff;
		}

		iter->next = NULL;
	}

	return iter;
}

/**
 * Handle requests timeout
 * @param tail Pointer to request queue tail pointer
 * @param t Time since last call in seconds
 */
static void
mqtt_request_time_elapsed(struct mqtt_request_t** tail, u8_t t)
{
	struct mqtt_request_t* r = *tail;
	LWIP_ASSERT("mqtt_request_time_elapsed: tail != NULL", tail != NULL);

	while(t > 0 && r != NULL) {
		if(t >= r->timeout_diff) {
			t -= (u8_t)r->timeout_diff;
			/* Unchain */
			*tail = r->next;

			/* Notify upper layer about timeout */
			if(r->cb != NULL) {
				r->cb(r->arg, ERR_TIMEOUT);
			}

			mqtt_delete_request(r);
			/* Tail might be be modified in callback, so re-read it in every iteration */
			r = *(struct mqtt_request_t* const volatile*)tail;
		} else {
			r->timeout_diff -= t;
			t = 0;
		}
	}
}

/**
 * Free all request items
 * @param tail Pointer to request queue tail pointer
 */
static void
mqtt_clear_requests(struct mqtt_request_t** tail)
{
	struct mqtt_request_t* iter, *next;
	LWIP_ASSERT("mqtt_clear_requests: tail != NULL", tail != NULL);

	for(iter = *tail; iter != NULL; iter = next) {
		next = iter->next;
		mqtt_delete_request(iter);
	}

	*tail = NULL;
}
/**
 * Initialize all request items
 * @param r_objs Pointer to request objects
 */
static void
mqtt_init_requests(struct mqtt_request_t* r_objs)
{
	u8_t n;
	LWIP_ASSERT("mqtt_init_requests: r_objs != NULL", r_objs != NULL);

	for(n = 0; n < MQTT_REQ_MAX_IN_FLIGHT; n++) {
		/* Item pointing to itself indicates unused */
		r_objs[n].next = &r_objs[n];
	}
}

/*--------------------------------------------------------------------------------------------------------------------- */
/* Output message build helpers */


static void
mqtt_output_append_u8(struct mqtt_ringbuf_t* rb, u8_t value)
{
	mqtt_ringbuf_put(rb, value);
}

static
void mqtt_output_append_u16(struct mqtt_ringbuf_t* rb, u16_t value)
{
	mqtt_ringbuf_put(rb, value >> 8);
	mqtt_ringbuf_put(rb, value & 0xff);
}

static void
mqtt_output_append_buf(struct mqtt_ringbuf_t* rb, const void* data, u16_t length)
{
	u16_t n;

	for(n = 0; n < length; n++) {
		mqtt_ringbuf_put(rb, ((const u8_t*)data)[n]);
	}
}

static void
mqtt_output_append_string(struct mqtt_ringbuf_t* rb, const char* str, u16_t length)
{
	u16_t n;
	mqtt_ringbuf_put(rb, length >> 8);
	mqtt_ringbuf_put(rb, length & 0xff);

	for(n = 0; n < length; n++) {
		mqtt_ringbuf_put(rb, str[n]);
	}
}

/**
 * Append fixed header
 * @param rb Output ring buffer
 * @param msg_type see enum mqtt_message_type
 * @param dup MQTT DUP flag
 * @param qos MQTT QoS field
 * @param retain MQTT retain flag
 * @param r_length Remaining length after fixed header
 */

static void
mqtt_output_append_fixed_header(struct mqtt_ringbuf_t* rb, u8_t msg_type, u8_t dup,
                                u8_t qos, u8_t retain, u16_t r_length)
{
	/* Start with control byte */
	mqtt_output_append_u8(rb, (((msg_type & 0x0f) << 4) | ((dup & 1) << 3) | ((qos & 3) << 1) | (retain & 1)));

	/* Encode remaining length field */
	do {
		mqtt_output_append_u8(rb, (r_length & 0x7f) | (r_length >= 128 ? 0x80 : 0));
		r_length >>= 7;
	} while(r_length > 0);
}


/**
 * Check output buffer space
 * @param rb Output ring buffer
 * @param r_length Remaining length after fixed header
 * @return 1 if message will fit, 0 if not enough buffer space
 */
static u8_t
mqtt_output_check_space(struct mqtt_ringbuf_t* rb, u16_t r_length)
{
	/* Start with length of type byte + remaining length */
	u16_t total_len = 1 + r_length;

	LWIP_ASSERT("mqtt_output_check_space: rb != NULL", rb != NULL);

	/* Calculate number of required bytes to contain the remaining bytes field and add to total*/
	do {
		total_len++;
		r_length >>= 7;
	} while(r_length > 0);

	return (total_len <= mqtt_ringbuf_free(rb));
}


/**
 * Close connection to server
 * @param client MQTT client
 * @param reason Reason for disconnection
 */
static void
mqtt_close(mqtt_client_t* client, mqtt_connection_status_t reason)
{
	LWIP_ASSERT("mqtt_close: client != NULL", client != NULL);

	/* Bring down TCP connection if not already done */
	if(client->conn != NULL) {
		err_t res;
		tcp_recv(client->conn, NULL);
		tcp_err(client->conn,  NULL);
		tcp_sent(client->conn, NULL);
		res = tcp_close(client->conn);

		if(res != ERR_OK) {
			tcp_abort(client->conn);
			LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_close: Close err=%s\n", lwip_strerr(res)));
		}

		client->conn = NULL;
	}

	/* Remove all pending requests */
	mqtt_clear_requests(&client->pend_req_queue);
	/* Stop cyclic timer */
	sys_untimeout(mqtt_cyclic_timer, client);

	/* Notify upper layer of disconnection if changed state */
	if(client->conn_state != TCP_DISCONNECTED) {

		client->conn_state = TCP_DISCONNECTED;

		if(client->connect_cb != NULL) {
			client->connect_cb(client, client->connect_arg, reason);
		}
	}
}


/**
 * Interval timer, called every MQTT_CYCLIC_TIMER_INTERVAL seconds in MQTT_CONNECTING and MQTT_CONNECTED states
 * @param arg MQTT client
 */
static void
mqtt_cyclic_timer(void* arg)
{
	u8_t restart_timer = 1;
	mqtt_client_t* client = (mqtt_client_t*)arg;
	LWIP_ASSERT("mqtt_cyclic_timer: client != NULL", client != NULL);

	if(client->conn_state == MQTT_CONNECTING) {
		client->cyclic_tick++;

		if((client->cyclic_tick * MQTT_CYCLIC_TIMER_INTERVAL) >= MQTT_CONNECT_TIMOUT) {
			LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_cyclic_timer: CONNECT attempt to server timed out\n"));
			/* Disconnect TCP */
			mqtt_close(client, MQTT_CONNECT_TIMEOUT);
			restart_timer = 0;
		}
	} else if(client->conn_state == MQTT_CONNECTED) {
		/* Handle timeout for pending requests */
		mqtt_request_time_elapsed(&client->pend_req_queue, MQTT_CYCLIC_TIMER_INTERVAL);

		/* keep_alive > 0 means keep alive functionality shall be used */
		if(client->keep_alive > 0) {

			client->server_watchdog++;

			/* If reception from server has been idle for 1.5*keep_alive time, server is considered unresponsive */
			if((client->server_watchdog * MQTT_CYCLIC_TIMER_INTERVAL) > (client->keep_alive + client->keep_alive / 2)) {
				LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_cyclic_timer: Server incoming keep-alive timeout\n"));
				mqtt_close(client, MQTT_CONNECT_TIMEOUT);
				restart_timer = 0;
			}

			/* If time for a keep alive message to be sent, transmission has been idle for keep_alive time */
			if((client->cyclic_tick * MQTT_CYCLIC_TIMER_INTERVAL) >= client->keep_alive) {
				LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_cyclic_timer: Sending keep-alive message to server\n"));

				if(mqtt_output_check_space(&client->output, 0) != 0) {
					mqtt_output_append_fixed_header(&client->output, MQTT_MSG_TYPE_PINGREQ, 0, 0, 0, 0);
					client->cyclic_tick = 0;
				}
			} else {
				client->cyclic_tick++;
			}
		}
	} else {
		LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_cyclic_timer: Timer should not be running in state %d\n", client->conn_state));
		restart_timer = 0;
	}

	if(restart_timer) {
		sys_timeout(MQTT_CYCLIC_TIMER_INTERVAL * 1000, mqtt_cyclic_timer, arg);
	}
}


/**
 * Send PUBACK, PUBREC or PUBREL response message
 * @param client MQTT client
 * @param msg PUBACK, PUBREC or PUBREL
 * @param pkt_id Packet identifier
 * @param qos QoS value
 * @return ERR_OK if successful, ERR_MEM if out of memory
 */
static err_t
pub_ack_rec_rel_response(mqtt_client_t* client, u8_t msg, u16_t pkt_id, u8_t qos)
{
	err_t err = ERR_OK;

	if(mqtt_output_check_space(&client->output, 2)) {
		mqtt_output_append_fixed_header(&client->output, msg, 0, qos, 0, 2);
		mqtt_output_append_u16(&client->output, pkt_id);
		mqtt_output_send(&client->output, client->conn);
	} else {
		LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("pub_ack_rec_rel_response: OOM creating response: %s with pkt_id: %d\n",
		                               mqtt_msg_type_to_str(msg), pkt_id));
		err = ERR_MEM;
	}

	return err;
}

/**
 * Subscribe response from server
 * @param r Matching request
 * @param result Result code from server
 */
static void
mqtt_incomming_suback(struct mqtt_request_t* r, u8_t result)
{
	if(r->cb != NULL) {
		r->cb(r->arg, result < 3 ? ERR_OK : ERR_ABRT);
	}
}


/**
 * Complete MQTT message received or buffer full
 * @param client MQTT client
 * @param fixed_hdr_idx header index
 * @param length length received part
 * @param remaining_length Remaining length of complete message
 */
static mqtt_connection_status_t
mqtt_message_received(mqtt_client_t* client, u8_t fixed_hdr_idx, u16_t length, u32_t remaining_length)
{
	mqtt_connection_status_t res = MQTT_CONNECT_ACCEPTED;

	u8_t* var_hdr_payload = client->rx_buffer + fixed_hdr_idx;

	/* Control packet type */
	u8_t pkt_type = MQTT_CTL_PACKET_TYPE(client->rx_buffer[0]);
	u16_t pkt_id = 0;

	if(pkt_type == MQTT_MSG_TYPE_CONNACK) {
		if(client->conn_state == MQTT_CONNECTING) {
			/* Get result code from CONNACK */
			res = (mqtt_connection_status_t)var_hdr_payload[1];
			LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_message_received: Connect response code %d\n", res));

			if(res == MQTT_CONNECT_ACCEPTED) {
				/* Reset cyclic_tick when changing to connected state */
				client->cyclic_tick = 0;
				client->conn_state = MQTT_CONNECTED;

				/* Notify upper layer */
				if(client->connect_cb != 0) {
					client->connect_cb(client, client->connect_arg, res);
				}
			}
		} else {
			LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_message_received: Received CONNACK in connected state\n"));
		}
	} else if(pkt_type == MQTT_MSG_TYPE_PINGRESP) {
		LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_message_received: Received PINGRESP from server\n"));

	} else if(pkt_type == MQTT_MSG_TYPE_PUBLISH) {
		u16_t payload_offset = 0;
		u16_t payload_length = length;
		u8_t qos = MQTT_CTL_PACKET_QOS(client->rx_buffer[0]);

		if(client->msg_idx <= MQTT_VAR_HEADER_BUFFER_LEN) {
			/* Should have topic and pkt id*/
			uint8_t* topic;
			uint16_t after_topic;
			u8_t bkp;
			u16_t topic_len = var_hdr_payload[0];
			topic_len = (topic_len << 8) + (u16_t)(var_hdr_payload[1]);

			topic = var_hdr_payload + 2;
			after_topic = 2 + topic_len;

			/* Check length, add one byte even for QoS 0 so that zero termination will fit */
			if((after_topic + (qos ? 2 : 1)) > length) {
				LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_message_received: Receive buffer can not fit topic + pkt_id\n"));
				goto out_disconnect;
			}

			/* id for QoS 1 and 2 */
			if(qos > 0) {
				client->inpub_pkt_id = ((u16_t)var_hdr_payload[after_topic] << 8) + (u16_t)var_hdr_payload[after_topic + 1];
				after_topic += 2;
			} else {
				client->inpub_pkt_id = 0;
			}

			/* Take backup of byte after topic */
			bkp = topic[topic_len];
			/* Zero terminate string */
			topic[topic_len] = 0;
			/* Payload data remaining in receive buffer */
			payload_length = length - after_topic;
			payload_offset = after_topic;

			LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_incomming_publish: Received message with QoS %d at topic: %s, payload length %d\n",
			                               qos, topic, remaining_length + payload_length));

			if(client->pub_cb != NULL) {
				client->pub_cb(client->inpub_arg, (const char*)topic, remaining_length + payload_length);
			}

			/* Restore byte after topic */
			topic[topic_len] = bkp;
		}

		if(payload_length > 0 || remaining_length == 0) {
			client->data_cb(client->inpub_arg, var_hdr_payload + payload_offset, payload_length, remaining_length == 0 ? MQTT_DATA_FLAG_LAST : 0);

			/* Reply if QoS > 0 */
			if(remaining_length == 0 && qos > 0) {
				/* Send PUBACK for QoS 1 or PUBREC for QoS 2 */
				u8_t resp_msg = (qos == 1) ? MQTT_MSG_TYPE_PUBACK : MQTT_MSG_TYPE_PUBREC;
				LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_incomming_publish: Sending publish response: %s with pkt_id: %d\n",
				                               mqtt_msg_type_to_str(resp_msg), client->inpub_pkt_id));
				pub_ack_rec_rel_response(client, resp_msg, client->inpub_pkt_id, 0);
			}
		}
	} else {
		/* Get packet identifier */
		pkt_id = (u16_t)var_hdr_payload[0] << 8;
		pkt_id |= (u16_t)var_hdr_payload[1];

		if(pkt_id == 0) {
			LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_message_received: Got message with illegal packet identifier: 0\n"));
			goto out_disconnect;
		}

		if(pkt_type == MQTT_MSG_TYPE_PUBREC) {
			LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_message_received: PUBREC, sending PUBREL with pkt_id: %d\n", pkt_id));
			pub_ack_rec_rel_response(client, MQTT_MSG_TYPE_PUBREL, pkt_id, 1);

		} else if(pkt_type == MQTT_MSG_TYPE_PUBREL) {
			LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_message_received: PUBREL, sending PUBCOMP response with pkt_id: %d\n", pkt_id));
			pub_ack_rec_rel_response(client, MQTT_MSG_TYPE_PUBCOMP, pkt_id, 0);

		} else if(pkt_type == MQTT_MSG_TYPE_SUBACK || pkt_type == MQTT_MSG_TYPE_UNSUBACK ||
		          pkt_type == MQTT_MSG_TYPE_PUBCOMP || pkt_type == MQTT_MSG_TYPE_PUBACK) {
			struct mqtt_request_t* r = mqtt_take_request(&client->pend_req_queue, pkt_id);

			if(r != NULL) {
				LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_message_received: %s response with id %d\n", mqtt_msg_type_to_str(pkt_type), pkt_id));

				if(pkt_type == MQTT_MSG_TYPE_SUBACK) {
					if(length < 3) {
						LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_message_received: To small SUBACK packet\n"));
						goto out_disconnect;
					} else {
						mqtt_incomming_suback(r, var_hdr_payload[2]);
					}
				} else if(r->cb != NULL) {
					r->cb(r->arg, ERR_OK);
				}

				mqtt_delete_request(r);
			} else {
				LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_message_received: Received %s reply, with wrong pkt_id: %d\n", mqtt_msg_type_to_str(pkt_type), pkt_id));
			}
		} else {
			LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_message_received: Received unknown message type: %d\n", pkt_type));
			goto out_disconnect;
		}
	}

	return res;
out_disconnect:
	return MQTT_CONNECT_DISCONNECTED;
}


/**
 * MQTT incoming message parser
 * @param client MQTT client
 * @param p PBUF chain of received data
 * @return Connection status
 */
static mqtt_connection_status_t
mqtt_parse_incoming(mqtt_client_t* client, struct pbuf* p)
{
	u16_t in_offset = 0;
	u32_t msg_rem_len = 0;
	u8_t fixed_hdr_idx = 0;
	u8_t b = 0;

	while(p->tot_len > in_offset) {
		if((fixed_hdr_idx < 2) || ((b & 0x80) != 0)) {

			if(fixed_hdr_idx < client->msg_idx) {
				b = client->rx_buffer[fixed_hdr_idx];
			} else {
				b = pbuf_get_at(p, in_offset++);
				client->rx_buffer[client->msg_idx++] = b;
			}

			fixed_hdr_idx++;

			if(fixed_hdr_idx >= 2) {
				msg_rem_len |= (u32_t)(b & 0x7f) << ((fixed_hdr_idx - 2) * 7);

				if((b & 0x80) == 0) {
					LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_parse_incoming: Remaining length after fixed header: %d\n", msg_rem_len));

					if(msg_rem_len == 0) {
						/* Complete message with no extra headers of payload received */
						mqtt_message_received(client, fixed_hdr_idx, 0, 0);
						client->msg_idx = 0;
						fixed_hdr_idx = 0;
					} else {
						/* Bytes remaining in message */
						msg_rem_len = (msg_rem_len + fixed_hdr_idx) - client->msg_idx;
					}
				}
			}
		} else {
			u16_t cpy_len, cpy_start, buffer_space;

			cpy_start = (client->msg_idx - fixed_hdr_idx) % (MQTT_VAR_HEADER_BUFFER_LEN - fixed_hdr_idx) + fixed_hdr_idx;

			/* Allow to copy the lesser one of available length in input data or bytes remaining in message */
			cpy_len = (u16_t)LWIP_MIN((u16_t)(p->tot_len - in_offset), msg_rem_len);

			/* Limit to available space in buffer */
			buffer_space = MQTT_VAR_HEADER_BUFFER_LEN - cpy_start;

			if(cpy_len > buffer_space) {
				cpy_len = buffer_space;
			}

			pbuf_copy_partial(p, client->rx_buffer + cpy_start, cpy_len, in_offset);

			/* Advance get and put indexes  */
			client->msg_idx += cpy_len;
			in_offset += cpy_len;
			msg_rem_len -= cpy_len;

			LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_parse_incoming: msg_idx: %d, cpy_len: %d, remaining %d\n", client->msg_idx, cpy_len, msg_rem_len));

			if(msg_rem_len == 0 || cpy_len == buffer_space) {
				/* Whole message received or buffer is full */
				mqtt_connection_status_t res = mqtt_message_received(client, fixed_hdr_idx, (cpy_start + cpy_len) - fixed_hdr_idx, msg_rem_len);

				if(res != MQTT_CONNECT_ACCEPTED) {
					return res;
				}

				if(msg_rem_len == 0) {
					/* Reset parser state */
					client->msg_idx = 0;
					/* msg_tot_len = 0; */
					fixed_hdr_idx = 0;
				}
			}
		}
	}

	return MQTT_CONNECT_ACCEPTED;
}


/**
 * TCP received callback function. @see tcp_recv_fn
 * @param arg MQTT client
 * @param p PBUF chain of received data
 * @param err Passed as return value if not ERR_OK
 * @return ERR_OK or err passed into callback
 */
static err_t
mqtt_tcp_recv_cb(void* arg, struct tcp_pcb* pcb, struct pbuf* p, err_t err)
{
	mqtt_client_t* client = (mqtt_client_t*)arg;
	LWIP_ASSERT("mqtt_tcp_recv_cb: client != NULL", client != NULL);
	LWIP_ASSERT("mqtt_tcp_recv_cb: client->conn == pcb", client->conn == pcb);

	if(p == NULL) {
		LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_tcp_recv_cb: Recv pbuf=NULL, remote has closed connection\n"));
		mqtt_close(client, MQTT_CONNECT_DISCONNECTED);
	} else {
		mqtt_connection_status_t res;

		if(err != ERR_OK) {
			LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_tcp_recv_cb: Recv err=%d\n", err));
			pbuf_free(p);
			return err;
		}

		/* Tell remote that data has been received */
		tcp_recved(pcb, p->tot_len);
		res = mqtt_parse_incoming(client, p);
		pbuf_free(p);

		if(res != MQTT_CONNECT_ACCEPTED) {
			mqtt_close(client, res);
		}

		/* If keep alive functionality is used */
		if(client->keep_alive != 0) {
			/* Reset server alive watchdog */
			client->server_watchdog = 0;
		}

	}

	return ERR_OK;
}


/**
 * TCP data sent callback function. @see tcp_sent_fn
 * @param arg MQTT client
 * @param tpcb TCP connection handle
 * @param len Number of bytes sent
 * @return ERR_OK
 */
static err_t
mqtt_tcp_sent_cb(void* arg, struct tcp_pcb* tpcb, u16_t len)
{
	mqtt_client_t* client = (mqtt_client_t*)arg;

	LWIP_UNUSED_ARG(tpcb);
	LWIP_UNUSED_ARG(len);

	if(client->conn_state == MQTT_CONNECTED) {
		struct mqtt_request_t* r;

		/* Reset keep-alive send timer and server watchdog */
		client->cyclic_tick = 0;
		client->server_watchdog = 0;

		/* QoS 0 publish has no response from server, so call its callbacks here */
		while((r = mqtt_take_request(&client->pend_req_queue, 0)) != NULL) {
			LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_tcp_sent_cb: Calling QoS 0 publish complete callback\n"));

			if(r->cb != NULL) {
				r->cb(r->arg, ERR_OK);
			}

			mqtt_delete_request(r);
		}

		/* Try send any remaining buffers from output queue */
		mqtt_output_send(&client->output, client->conn);
	}

	return ERR_OK;
}

/**
 * TCP error callback function. @see tcp_err_fn
 * @param arg MQTT client
 * @param err Error encountered
 */
static void
mqtt_tcp_err_cb(void* arg, err_t err)
{
	mqtt_client_t* client = (mqtt_client_t*)arg;
	LWIP_UNUSED_ARG(err); /* only used for debug output */
	LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_tcp_err_cb: TCP error callback: error %d, arg: %p\n", err, arg));
	LWIP_ASSERT("mqtt_tcp_err_cb: client != NULL", client != NULL);
	/* Set conn to null before calling close as pcb is already deallocated*/
	client->conn = 0;
	mqtt_close(client, MQTT_CONNECT_DISCONNECTED);
}

/**
 * TCP poll callback function. @see tcp_poll_fn
 * @param arg MQTT client
 * @param tpcb TCP connection handle
 * @return err ERR_OK
 */
static err_t
mqtt_tcp_poll_cb(void* arg, struct tcp_pcb* tpcb)
{
	mqtt_client_t* client = (mqtt_client_t*)arg;

	if(client->conn_state == MQTT_CONNECTED) {
		/* Try send any remaining buffers from output queue */
		mqtt_output_send(&client->output, tpcb);
	}

	return ERR_OK;
}

/**
 * TCP connect callback function. @see tcp_connected_fn
 * @param arg MQTT client
 * @param err Always ERR_OK, mqtt_tcp_err_cb is called in case of error
 * @return ERR_OK
 */
static err_t
mqtt_tcp_connect_cb(void* arg, struct tcp_pcb* tpcb, err_t err)
{
	mqtt_client_t* client = (mqtt_client_t*)arg;

	if(err != ERR_OK) {
		LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_tcp_connect_cb: TCP connect error %d\n", err));
		return err;
	}

	/* Initiate receiver state */
	client->msg_idx = 0;

	/* Setup TCP callbacks */
	tcp_recv(tpcb, mqtt_tcp_recv_cb);
	tcp_sent(tpcb, mqtt_tcp_sent_cb);
	tcp_poll(tpcb, mqtt_tcp_poll_cb, 2);

	LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_tcp_connect_cb: TCP connection established to server\n"));
	/* Enter MQTT connect state */
	client->conn_state = MQTT_CONNECTING;

	/* Start cyclic timer */
	sys_timeout(MQTT_CYCLIC_TIMER_INTERVAL * 1000, mqtt_cyclic_timer, client);
	client->cyclic_tick = 0;

	/* Start transmission from output queue, connect message is the first one out*/
	mqtt_output_send(&client->output, client->conn);

	return ERR_OK;
}



/*---------------------------------------------------------------------------------------------------- */
/* Public API */


/**
 * @ingroup mqtt
 * MQTT publish function.
 * @param client MQTT client
 * @param topic Publish topic string
 * @param payload Data to publish (NULL is allowed)
 * @param payload_length: Length of payload (0 is allowed)
 * @param qos Quality of service, 0 1 or 2
 * @param retain MQTT retain flag
 * @param cb Callback to call when publish is complete or has timed out
 * @param arg User supplied argument to publish callback
 * @return ERR_OK if successful
 *         ERR_CONN if client is disconnected
 *         ERR_MEM if short on memory
 */
err_t
mqtt_publish(mqtt_client_t* client, const char* topic, const void* payload, u16_t payload_length, u8_t qos, u8_t retain,
             mqtt_request_cb_t cb, void* arg)
{
	struct mqtt_request_t* r;
	u16_t pkt_id;
	size_t topic_strlen;
	size_t total_len;
	u16_t topic_len;
	u16_t remaining_length;

	LWIP_ASSERT("mqtt_publish: client != NULL", client);
	LWIP_ASSERT("mqtt_publish: topic != NULL", topic);
	LWIP_ERROR("mqtt_publish: TCP disconnected", (client->conn_state != TCP_DISCONNECTED), return ERR_CONN);

	topic_strlen = strlen(topic);
	LWIP_ERROR("mqtt_publish: topic length overflow", (topic_strlen <= (0xFFFF - 2)), return ERR_ARG);
	topic_len = (u16_t)topic_strlen;
	total_len = 2 + topic_len + payload_length;
	LWIP_ERROR("mqtt_publish: total length overflow", (total_len <= 0xFFFF), return ERR_ARG);
	remaining_length = (u16_t)total_len;

	LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_publish: Publish with payload length %d to topic \"%s\"\n", payload_length, topic));

	if(qos > 0) {
		remaining_length += 2;
		/* Generate pkt_id id for QoS1 and 2 */
		pkt_id = msg_generate_packet_id(client);
	} else {
		/* Use reserved value pkt_id 0 for QoS 0 in request handle */
		pkt_id = 0;
	}

	r = mqtt_create_request(client->req_list, pkt_id, cb, arg);

	if(r == NULL) {
		return ERR_MEM;
	}

	if(mqtt_output_check_space(&client->output, remaining_length) == 0) {
		mqtt_delete_request(r);
		return ERR_MEM;
	}

	/* Append fixed header */
	mqtt_output_append_fixed_header(&client->output, MQTT_MSG_TYPE_PUBLISH, 0, qos, retain, remaining_length);

	/* Append Topic */
	mqtt_output_append_string(&client->output, topic, topic_len);

	/* Append packet if for QoS 1 and 2*/
	if(qos > 0) {
		mqtt_output_append_u16(&client->output, pkt_id);
	}

	/* Append optional publish payload */
	if((payload != NULL) && (payload_length > 0)) {
		mqtt_output_append_buf(&client->output, payload, payload_length);
	}

	mqtt_append_request(&client->pend_req_queue, r);
	mqtt_output_send(&client->output, client->conn);
	return ERR_OK;
}


/**
 * @ingroup mqtt
 * MQTT subscribe/unsubscribe function.
 * @param client MQTT client
 * @param topic topic to subscribe to
 * @param qos Quality of service, 0 1 or 2 (only used for subscribe)
 * @param cb Callback to call when subscribe/unsubscribe reponse is received
 * @param arg User supplied argument to publish callback
 * @param sub 1 for subscribe, 0 for unsubscribe
 * @return ERR_OK if successful, @see err_t enum for other results
 */
err_t
mqtt_sub_unsub(mqtt_client_t* client, const char* topic, u8_t qos, mqtt_request_cb_t cb, void* arg, u8_t sub)
{
	size_t topic_strlen;
	size_t total_len;
	u16_t topic_len;
	u16_t remaining_length;
	u16_t pkt_id;
	struct mqtt_request_t* r;

	LWIP_ASSERT("mqtt_sub_unsub: client != NULL", client);
	LWIP_ASSERT("mqtt_sub_unsub: topic != NULL", topic);

	topic_strlen = strlen(topic);
	LWIP_ERROR("mqtt_sub_unsub: topic length overflow", (topic_strlen <= (0xFFFF - 2)), return ERR_ARG);
	topic_len = (u16_t)topic_strlen;
	/* Topic string, pkt_id, qos for subscribe */
	total_len =  topic_len + 2 + 2 + (sub != 0);
	LWIP_ERROR("mqtt_sub_unsub: total length overflow", (total_len <= 0xFFFF), return ERR_ARG);
	remaining_length = (u16_t)total_len;

	LWIP_ASSERT("mqtt_sub_unsub: qos < 3", qos < 3);

	if(client->conn_state == TCP_DISCONNECTED) {
		LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_sub_unsub: Can not (un)subscribe in disconnected state\n"));
		return ERR_CONN;
	}

	pkt_id = msg_generate_packet_id(client);
	r = mqtt_create_request(client->req_list, pkt_id, cb, arg);

	if(r == NULL) {
		return ERR_MEM;
	}

	if(mqtt_output_check_space(&client->output, remaining_length) == 0) {
		mqtt_delete_request(r);
		return ERR_MEM;
	}

	LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_sub_unsub: Client (un)subscribe to topic \"%s\", id: %d\n", topic, pkt_id));

	mqtt_output_append_fixed_header(&client->output, sub ? MQTT_MSG_TYPE_SUBSCRIBE : MQTT_MSG_TYPE_UNSUBSCRIBE, 0, 1, 0, remaining_length);
	/* Packet id */
	mqtt_output_append_u16(&client->output, pkt_id);
	/* Topic */
	mqtt_output_append_string(&client->output, topic, topic_len);

	/* QoS */
	if(sub != 0) {
		mqtt_output_append_u8(&client->output, LWIP_MIN(qos, 2));
	}

	mqtt_append_request(&client->pend_req_queue, r);
	mqtt_output_send(&client->output, client->conn);
	return ERR_OK;
}


/**
 * @ingroup mqtt
 * Set callback to handle incoming publish requests from server
 * @param client MQTT client
 * @param pub_cb Callback invoked when publish starts, contain topic and total length of payload
 * @param data_cb Callback for each fragment of payload that arrives
 * @param arg User supplied argument to both callbacks
 */
void
mqtt_set_inpub_callback(mqtt_client_t* client, mqtt_incoming_publish_cb_t pub_cb,
                        mqtt_incoming_data_cb_t data_cb, void* arg)
{
	LWIP_ASSERT("mqtt_set_inpub_callback: client != NULL", client != NULL);
	client->data_cb = data_cb;
	client->pub_cb = pub_cb;
	client->inpub_arg = arg;
}

/**
 * @ingroup mqtt
 * Create a new MQTT client instance
 * @return Pointer to instance on success, NULL otherwise
 */
mqtt_client_t*
mqtt_client_new(void)
{
	mqtt_client_t* client = (mqtt_client_t*)mem_malloc(sizeof(mqtt_client_t));

	if(client != NULL) {
		memset(client, 0, sizeof(mqtt_client_t));
	}

	return client;
}


/**
 * @ingroup mqtt
 * Connect to MQTT server
 * @param client MQTT client
 * @param ip_addr Server IP
 * @param port Server port
 * @param cb Connection state change callback
 * @param arg User supplied argument to connection callback
 * @param client_info Client identification and connection options
 * @return ERR_OK if successful, @see err_t enum for other results
 */
err_t
mqtt_client_connect(mqtt_client_t* client, const ip_addr_t* ip_addr, u16_t port, mqtt_connection_cb_t cb, void* arg,
                    const struct mqtt_connect_client_info_t* client_info)
{
	err_t err;
	size_t len;
	u16_t client_id_length;
	/* Length is the sum of 2+"MQTT", protocol level, flags and keep alive */
	u16_t remaining_length = 2 + 4 + 1 + 1 + 2;
	u8_t flags = 0, will_topic_len = 0, will_msg_len = 0;

	LWIP_ASSERT("mqtt_client_connect: client != NULL", client != NULL);
	LWIP_ASSERT("mqtt_client_connect: ip_addr != NULL", ip_addr != NULL);
	LWIP_ASSERT("mqtt_client_connect: client_info != NULL", client_info != NULL);
	LWIP_ASSERT("mqtt_client_connect: client_info->client_id != NULL", client_info->client_id != NULL);

	if(client->conn_state != TCP_DISCONNECTED) {
		LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_client_connect: Already connected\n"));
		return ERR_ISCONN;
	}

	/* Wipe clean */
	memset(client, 0, sizeof(mqtt_client_t));
	client->connect_arg = arg;
	client->connect_cb = cb;
	client->keep_alive = client_info->keep_alive;
	mqtt_init_requests(client->req_list);

	/* Build connect message */
	if(client_info->will_topic != NULL && client_info->will_msg != NULL) {
		flags |= MQTT_CONNECT_FLAG_WILL;
		flags |= (client_info->will_qos & 3) << 3;

		if(client_info->will_retain) {
			flags |= MQTT_CONNECT_FLAG_WILL_RETAIN;
		}

		len = strlen(client_info->will_topic);
		LWIP_ERROR("mqtt_client_connect: client_info->will_topic length overflow", len <= 0xFF, return ERR_VAL);
		LWIP_ERROR("mqtt_client_connect: client_info->will_topic length must be > 0", len > 0, return ERR_VAL);
		will_topic_len = (u8_t)len;
		len = strlen(client_info->will_msg);
		LWIP_ERROR("mqtt_client_connect: client_info->will_msg length overflow", len <= 0xFF, return ERR_VAL);
		will_msg_len = (u8_t)len;
		len = remaining_length + 2 + will_topic_len + 2 + will_msg_len;
		LWIP_ERROR("mqtt_client_connect: remaining_length overflow", len <= 0xFFFF, return ERR_VAL);
		remaining_length = (u16_t)len;
	}

	/* Don't complicate things, always connect using clean session */
	flags |= MQTT_CONNECT_FLAG_CLEAN_SESSION;

	len = strlen(client_info->client_id);
	LWIP_ERROR("mqtt_client_connect: client_info->client_id length overflow", len <= 0xFFFF, return ERR_VAL);
	client_id_length = (u16_t)len;
	len = remaining_length + 2 + client_id_length;
	LWIP_ERROR("mqtt_client_connect: remaining_length overflow", len <= 0xFFFF, return ERR_VAL);
	remaining_length = (u16_t)len;

	if(mqtt_output_check_space(&client->output, remaining_length) == 0) {
		return ERR_MEM;
	}

	client->conn = tcp_new();

	if(client->conn == NULL) {
		return ERR_MEM;
	}

	/* Set arg pointer for callbacks */
	tcp_arg(client->conn, client);
	/* Any local address, pick random local port number */
	err = tcp_bind(client->conn, IP_ADDR_ANY, 0);

	if(err != ERR_OK) {
		LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_client_connect: Error binding to local ip/port, %d\n", err));
		goto tcp_fail;
	}

	LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_client_connect: Connecting to host: %s at port:%"U16_F"\n", ipaddr_ntoa(ip_addr), port));

	/* Connect to server */
	err = tcp_connect(client->conn, ip_addr, port, mqtt_tcp_connect_cb);

	if(err != ERR_OK) {
		LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_client_connect: Error connecting to remote ip/port, %d\n", err));
		goto tcp_fail;
	}

	/* Set error callback */
	tcp_err(client->conn, mqtt_tcp_err_cb);
	client->conn_state = TCP_CONNECTING;

	/* Append fixed header */
	mqtt_output_append_fixed_header(&client->output, MQTT_MSG_TYPE_CONNECT, 0, 0, 0, remaining_length);
	/* Append Protocol string */
	mqtt_output_append_string(&client->output, "MQTT", 4);
	/* Append Protocol level */
	mqtt_output_append_u8(&client->output, 4);
	/* Append connect flags */
	mqtt_output_append_u8(&client->output, flags);
	/* Append keep-alive */
	mqtt_output_append_u16(&client->output, client_info->keep_alive);
	/* Append client id */
	mqtt_output_append_string(&client->output, client_info->client_id, client_id_length);

	/* Append will message if used */
	if((flags & MQTT_CONNECT_FLAG_WILL) != 0) {
		mqtt_output_append_string(&client->output, client_info->will_topic, will_topic_len);
		mqtt_output_append_string(&client->output, client_info->will_msg, will_msg_len);
	}

	return ERR_OK;

tcp_fail:
	tcp_abort(client->conn);
	client->conn = NULL;
	return err;
}


/**
 * @ingroup mqtt
 * Disconnect from MQTT server
 * @param client MQTT client
 */
void
mqtt_disconnect(mqtt_client_t* client)
{
	LWIP_ASSERT("mqtt_disconnect: client != NULL", client);

	/* If connection in not already closed */
	if(client->conn_state != TCP_DISCONNECTED) {
		/* Set conn_state before calling mqtt_close to prevent callback from being called */
		client->conn_state = TCP_DISCONNECTED;
		mqtt_close(client, (mqtt_connection_status_t)0);
	}
}

/**
 * @ingroup mqtt
 * Check connection with server
 * @param client MQTT client
 * @return 1 if connected to server, 0 otherwise
 */
u8_t
mqtt_client_is_connected(mqtt_client_t* client)
{
	LWIP_ASSERT("mqtt_client_is_connected: client != NULL", client);
	return client->conn_state == MQTT_CONNECTED;
}

#endif /* LWIP_TCP && LWIP_CALLBACK_API */
